Several types of fire extinguishers have been employed for discharging dry chemical extinguishing agents. One type is known as the stored pressure type where dry chemical is maintained in a container under pressure. To release the dry chemical, a valve on the container is opened and the dry chemical is discharged through a nozzle.
Another type, for larger fires, has the container mounted on a vehicle to be taken to the site of the fire where the dry chemical, under stored pressure, is discharged through a length of hose having a nozzle at the end.
Still another type is known as the cartridge type. In this type, the dry chemical is maintained in a storage container and a suitable supply of gas such as compressed carbon dioxide, nitrogen, etc. is maintained in a cartridge connected to the container. Upon actuation of the device, the gas is fed into the dry chemical container to fluidize or aerate the dry chemical. Upon opening a valve, the fluidized dry chemical is then fed from the container to a hand manipulated nozzle which is aimed at the fire. This type has been disclosed in U.S. Pat. 2,531,123 to Guise et al.
The containers for these dry chemical type extinguishers have heretofore been made of metals, such as brass, steel, stainless steel and aluminum. As such, they suffer the disadvantages of being non-transparent, relatively heavy, and economically impractical to be disposable. Furthermore, to recharge these extinguishers, it is normally required that they be returned to a factory or service representative for replacement of the dry chemical agent and either repressurizing the container or replacement of the gas cartridge.
While pressure gages are normally used in the stored pressure types as an indication of whether or not the extinguisher has been used, the opaqueness of the containers affords no indication as to the presence or absence of the dry chemical agent.